The present invention is directed to a clamping chuck for drill bits, chisel bits and the like for use in a drilling tool with clamping jaws radially displaceably mounted in a guide sleeve, and a setting sleeve encircling the jaws and the guide sleeve and being axially displaceable relative to the guide sleeve. The setting sleeve and the clamping jaws have cooperating contacting surfaces inclined obliquely relative to the axis of the guide sleeve.
Chucks of the above type serve to clamp bits in a drilling tool where the bits have shanks of different diameters. The radial adjustment of the jaws is effected by axial displacement of the setting sleeve. The jaws slide relative to the cooperating surfaces on the setting sleeve. Special means are required so that the jaws follow the movement of the setting sleeve during inward or outward displacement.
In known chucks the movement of the clamping jaws is effected by radially pressing the jaws outwardly by means of spring elements against the cooperating surfaces of the setting sleeve. Such spring elements can be pressure springs located between the jaws or in the form of a radially flexible ring extending through the jaws. Since such elements do not provide a positive guidance of the jaws, it is possible that the jaws may become stuck during adjustment due to interference within the chuck caused by drillings or drilling dust becoming lodged between the abutting surfaces of the setting sleeve and the jaws. Apart from the wear caused by such material, such obstruction leads to the unsatisfactory centering of the drill bit.
In other known clamping chucks, positive guidance between the jaws and the setting sleeve is obtained by providing the clamping jaws with a T-shaped cross-section and guiding the jaws in similarly shaped grooves in the setting sleeve. The fabrication of such T-shaped grooves in the setting sleeve is particularly costly especially with smaller sizes of clamping chucks.